Quando il relitto della nave Endurance di Ernest Shackleton è stato trovato a quasi 10.000 piedi sotto la superficie del Mare di Weddell in Antartide nel marzo 2022, si trovava a sole 4 miglia dalla sua ultima posizione conosciuta, come registrato dal capitano e navigatore della Endurance, Frank Worsley, a novembre 1915.

È un livello di precisione sorprendente per una posizione determinata con strumenti meccanici, tabelle di numeri di riferimento lunghe un libro e carta e penna.

La spedizione alla ricerca della nave aveva cercato un'area sottomarina di 150 miglia quadrate, un cerchio di 14 miglia di diametro. Nessuno sapeva quanto fosse stato preciso il calcolo della posizione di Worsley o quanto lontano avrebbe potuto viaggiare la nave durante l'affondamento.

Ma come storico dell'esplorazione antartica, non sono stato sorpreso di scoprire quanto fosse accurato Worsley, e immagino che non lo fossero nemmeno quelli che cercavano il relitto.

La navigazione è stata fondamentale

La Endurance aveva lasciato l'Inghilterra nell'agosto del 1914, con l'irlandese Shackleton che sperava di diventare il primo ad attraversare il continente antartico da una parte all'altra.

Ma non sono mai nemmeno sbarcati in Antartide. La nave rimase bloccata nel ghiaccio marino nel mare di Weddell nel gennaio 1915, costringendo gli uomini a scendere dalla nave nelle tende piantate nell'oceano ghiacciato vicino. La forza del ghiaccio schiacciò lentamente l'Endurance, affondandolo 10 mesi dopo e dando il via a quella che sarebbe diventata un'incredibile, e quasi incredibile, saga di sopravvivenza e navigazione da parte di Shackleton e del suo equipaggio.

La guida di Shackleton è diventata leggenda, così come il suo impegno a garantire che nessun uomo sia perso dal gruppo sotto il suo comando, sebbene tre membri del gruppo di 10 uomini della spedizione nel Mare di Ross siano morti.

Meno nota è l'importanza delle capacità di navigazione del 42enne Worsley, un neozelandese che aveva trascorso decenni nella Marina mercantile britannica e nella Royal Navy Reserve. Senza di lui, la storia della sopravvivenza di Shackleton sarebbe stata probabilmente molto diversa.

Segnare il tempo

La navigazione richiede la determinazione della posizione di una nave in latitudine e longitudine. La latitudine è facile da trovare dall'angolo del Sole sopra l'orizzonte a mezzogiorno.

La longitudine richiedeva di confrontare il mezzogiorno locale, il momento in cui il Sole era nel punto più alto, con l'ora effettiva in un altro luogo in cui la longitudine era già nota. La chiave era assicurarsi che la misurazione del tempo per quell'altra posizione fosse accurata.

Fare queste osservazioni astronomiche e fare i calcoli risultanti era già abbastanza difficile a terra. Sull'oceano, con pochi punti di terra fissi visibili, in mezzo al maltempo, era quasi impossibile.

Quindi la navigazione dipendeva in gran parte dalla "resa dei conti". Questo era il processo di calcolo della posizione di una nave utilizzando una posizione precedentemente determinata e incorporando le stime della velocità e della direzione in cui si stava muovendo la nave. Worsley lo definì "il calcolo della rotta e della distanza da parte del marinaio".

Mira alla terra

When the Endurance was crushed, the crew had to get themselves to safety, or die on an ice floe adrift somewhere in the Southern Ocean. In April 1916, six months after the Endurance sank, the sea ice on which they had camped began to break up. The 28 men and their remaining gear and supplies loaded into three lifeboats—the James Caird, Dudley Docker and Stancomb Wills—each named for major donors to the expedition.

Worsley was in charge of getting them to land. As the journey began, Shackleton "saw Worsley, as navigating officer, balancing himself on the gunwale of the Dudley Docker with his arm around the mast, ready to snap the sun. He got his observation and we waited eagerly while he worked out the sight."

To do that, he compared his measurement with the time on his chronometer and written tables of calculations.

And so began one of the most remarkable rescue missions in history. In a small open lifeboat, six men sailed 800 miles across some of the roughest seas on the planet to get help. We think they navigated with these instruments, on display in #PolarWorlds pic.twitter.com/4lxgzfR1BL

— Dr. Claire Warrior (@ClaireWarrior1) March 9, 2022

A last hope of survival

Once they managed to arrive on a little rocky strip called Elephant Island, off the coast of the Antarctic Peninsula, they still faced starvation. Shackleton believed that the only hope of survival lay in fetching help from elsewhere.

Worsley was ready. Before the Endurance was crushed, he had "worked out the courses and distances from the South Orkneys to South Georgia, the Falklands and Cape Horn, respectively, and from Elephant Island to the same places," he recalled in his memoir.

The men used parts of the other lifeboats to reinforce the James Caird for a long sea journey. Every day, Worsley "watched closely for the sun or stars to appear, to correct my chronometer, on the accuracy of which our lives and the success of the journey would depend."

On April 24, 1916, Worsley got "The first sunny day with a clear enough horizon to get a sight for rating my chronometer." That same day, he, Shackleton and four other men set off under sail in the 22.5-foot James Caird, carrying Worsley's chronometer, navigational books and two sextants, used for fixing the position of the Sun and stars.

The boat journey

These men, in this tiny boat, were going from one pinpoint of rock in the Southern Ocean to another, facing high winds, massive currents and choppy waters that could push them wildly astray or even sink them. The success of this voyage depended on Worsley's absolute accuracy, based on observations and estimations he made in the worst possible environmental conditions, while sleep-deprived and frostbitten.

They spent 16 days of "supreme strife amid heaving waters," as the boat sailed through some of the most dangerous sea conditions in the world, experiencing "mountainous" swells, rain, snow, sleet and hail. During that time, Worsley was able to get just four solid fixes on the boat's position. The rest was "a merry jest of guesswork" to determine where the wind and waves had taken them, and adjusting the steering accordingly.

The stakes were enormous—if he missed South Georgia, the next land was South Africa, 3,000 miles farther across more open ocean.

As Worsley wrote later:"Navigation is an art, but words fail to give my efforts a correct name. … Once, perhaps twice, a week the sun smiled a sudden wintry flicker, through storm-torn cloud. If ready for it, and smart, I caught it. The procedure was:I peered out from our burrow—precious sextant cuddled under my chest to prevent seas from falling on it. Sir Ernest stood by under the canvas with chronometer, pencil, and book. I shouted "Stand by," and knelt on the thwart—two men holding me up on either side. I brought the sun down to where the horizon ought to be and as the boat leaped frantically upward on the crest of a wave, snapped a good guess at the altitude and yelled "Stop." Sir Ernest took the time and I worked out the result. Then the fun started! Our fingers were so cold that he had to interpret his wobbly figures—my own so illegible that I had to recognize them by feats of memory."

On May 8, they saw floating seaweed and birds, and then spotted land. But they had arrived at South Georgia amid a hurricane, and for two days had to fight being driven by wind onto an island they had spent weeks desperately trying to reach.

Finally, they came ashore. Three of the six men, including Worsley, hiked across unmapped mountains and glaciers to reach a small settlement. Worsley joined a rescue boat back to get the other three. Shackleton later arranged a ship to collect the rest of the men from Elephant Island, all of whom had survived their own unimaginable hardships.

But the key to all of it, and indeed the recent discovery of the Endurance's wreck, was how Worsley had fought desperate conditions and still repeatedly managed to figure out where they were, where they were going and how to get there.